445 research outputs found
Recursive proof of the Bell-Kochen-Specker theorem in any dimension
We present a method to obtain sets of vectors proving the Bell-Kochen-Specker
theorem in dimension from a similar set in dimension (). As an application of the method we find the smallest proofs known in
dimension five (29 vectors), six (31) and seven (34), and different sets
matching the current record (36) in dimension eight.Comment: LaTeX, 7 page
Revisiting the effect of external fields in Axelrod's model of social dynamics
The study of the effects of spatially uniform fields on the steady-state
properties of Axelrod's model has yielded plenty of controversial results. Here
we re-examine the impact of this type of field for a selection of parameters
such that the field-free steady state of the model is heterogeneous or
multicultural. Analyses of both one and two-dimensional versions of Axelrod's
model indicate that, contrary to previous claims in the literature, the steady
state remains heterogeneous regardless of the value of the field strength.
Turning on the field leads to a discontinuous decrease on the number of
cultural domains, which we argue is due to the instability of zero-field
heterogeneous absorbing configurations. We find, however, that spatially
nonuniform fields that implement a consensus rule among the neighborhood of the
agents enforces homogenization. Although the overall effects of the fields are
essentially the same irrespective of the dimensionality of the model, we argue
that the dimensionality has a significant impact on the stability of the
field-free homogeneous steady state
Statistics of opinion domains of the majority-vote model on a square lattice
The existence of juxtaposed regions of distinct cultures in spite of the fact
that people's beliefs have a tendency to become more similar to each other's as
the individuals interact repeatedly is a puzzling phenomenon in the social
sciences. Here we study an extreme version of the frequency-dependent bias
model of social influence in which an individual adopts the opinion shared by
the majority of the members of its extended neighborhood, which includes the
individual itself. This is a variant of the majority-vote model in which the
individual retains its opinion in case there is a tie among the neighbors'
opinions. We assume that the individuals are fixed in the sites of a square
lattice of linear size and that they interact with their nearest neighbors
only.
Within a mean-field framework, we derive the equations of motion for the
density of individuals adopting a particular opinion in the single-site and
pair approximations. Although the single-site approximation predicts a single
opinion domain that takes over the entire lattice, the pair approximation
yields a qualitatively correct picture with the coexistence of different
opinion domains and a strong dependence on the initial conditions. Extensive
Monte Carlo simulations indicate the existence of a rich distribution of
opinion domains or clusters, the number of which grows with whereas the
size of the largest cluster grows with . The analysis of the sizes of
the opinion domains shows that they obey a power-law distribution for not too
large sizes but that they are exponentially distributed in the limit of very
large clusters. In addition, similarly to other well-known social influence
model -- Axelrod's model -- we found that these opinion domains are unstable to
the effect of a thermal-like noise
Mass media destabilizes the cultural homogeneous regime in Axelrod's model
An important feature of Axelrod's model for culture dissemination or social
influence is the emergence of many multicultural absorbing states, despite the
fact that the local rules that specify the agents interactions are explicitly
designed to decrease the cultural differences between agents. Here we
re-examine the problem of introducing an external, global interaction -- the
mass media -- in the rules of Axelrod's model: in addition to their
nearest-neighbors, each agent has a certain probability to interact with a
virtual neighbor whose cultural features are fixed from the outset. Most
surprisingly, this apparently homogenizing effect actually increases the
cultural diversity of the population. We show that, contrary to previous claims
in the literature, even a vanishingly small value of is sufficient to
destabilize the homogeneous regime for very large lattice sizes
Exciton-polaritons of a 2D semiconductor layer in a cylindrical microcavity
We describe exciton-polariton modes formed by the interaction between
excitons in a 2D layer of a transition metal dichalcogenide embedded in a
cylindrical microcavity and the microcavity photons. For this, an expression
for the excitonic susceptibility of a semiconductor disk placed in the symmetry
plane perpendicular to the axis of the microcavity is derived. Semiclassical
theory provides dispersion relations for the polariton modes, while the
quantum-mechanical treatment of a simplified model yields the Hopfield
coefficients, measuring the degree of exciton-photon mixing in the coupled
modes. The density of states (DOS) and its projection onto the photonic and the
excitonic subspaces are calculated taking monolayer MoS 2 embedded in a Si 3 N
4 cylinder as an example. The calculated results demonstrate a strong
enhancement, for certain frequencies, of the total and local DOS (Purcell
effect) caused by the presence of the 2D layer.We are grateful to Dr. Fernando de Leon for helpful discussion. Funding from the European Commission, within the project ”Graphene-Driven Revolutions in ICT and Beyond” (Ref. No. 696656), and from the Portuguese Foundation for Science and Technology (FCT) in the framework of the PTDC/NAN-OPT/29265/2017 Towards high speed optical devices by exploiting the unique electronic properties of engineered 2D materials project the Strategic Funding UID/FIS/04650/2019 is gratefully acknowledged. C. T-G acknowledges support from the Brazilian Agency CNPq
An electronic nose as a non-destructive analytical tool to identify the geographical origin of Portuguese olive oils from two adjacent regions
The geographical traceability of extra virgin olive oils (EVOO) is of paramount importance for oil chain actors and consumers. Oils produced in two adjacent Portuguese regions, Côa (36 oils) and Douro (31 oils), were evaluated and fulfilled the European legal thresholds for EVOO categorization. Compared to the Douro region, oils from Côa had higher total phenol contents (505 versus 279 mg GAE/kg) and greater oxidative stabilities (17.5 versus 10.6 h). The majority of Côa oils were fruity-green, bitter, and pungent oils. Conversely, Douro oils exhibited a more intense fruity-ripe and sweet sensation. Accordingly, different volatiles were detected, belonging to eight chemical families, from which aldehydes were the most abundant. Additionally, all oils were evaluated using a lab-made electronic nose, with metal oxide semiconductor sensors. The electrical fingerprints, together with principal component analysis, enabled the unsupervised recognition of the oils’ geographical origin, and their successful supervised linear discrimination (sensitivity of 98.5% and specificity of 98.4%; internal validation). The E-nose also quantified the contents of the two main volatile chemical classes (alcohols and aldehydes) and of the total volatiles content, for the studied olive oils split by geographical origin, using multivariate linear regression models (0.981 ≤ R2 ≤ 0.998 and 0.40 ≤ RMSE ≤ 2.79 mg/kg oil; internal validation). The E-nose-MOS was shown to be a fast, green, non-invasive and cost-effective tool for authenticating the geographical origin of the studied olive oils and to estimate the contents of the most abundant chemical classes of volatiles.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/2020 and UIDP/00690/2020), to CEB (UIDB/04469/2020) and to the Associate Laboratory SusTEC (LA/P/0007/2020). The authors are also grateful to the “Project OLIVECOA—Centenarian olive trees of Côa Valley region: rediscovering the past to valorize the future” (ref. COA/BRB/0035/2019), financed by FCT (Portugal). Nuno Rodrigues thanks the National funding by FCT- Foundation for Science and Technology, P.I., through the institutional scientific employment program-contract.info:eu-repo/semantics/publishedVersio
Sensory intensity assessment of olive oils using an electronic tongue
Olive oils may be commercialized as intense, medium or light, according to the intensity perception of fruitiness, bitterness and pungency attributes, assessed by a sensory panel. In this work, the capability of an electronic tongue to correctly classify olive oils according to the sensory intensity perception levels was evaluated. Cross-sensitivity and non-specific lipid polymeric membranes were used as sensors. The sensor device was firstly tested using quinine monohydrochloride standard solutions. Mean sensitivities of 14±2 to 25±6 mV/decade, depending on the type of plasticizer used in the lipid membranes, were obtained showing the device capability for evaluating bitterness. Then, linear discriminant models based on sub-sets of sensors, selected by a meta-heuristic simulated annealing algorithm, were established enabling to correctly classify 91% of olive oils according to their intensity sensory grade (leave-one-out cross-validation procedure). This capability was further evaluated using a repeated K-fold cross-validation procedure, showing that the electronic tongue allowed an average correct classification of 80% of the olive oils used for internal-validation. So, the electronic tongue can be seen as a taste sensor, allowing differentiating olive oils with different sensory intensities, and could be used as a preliminary, complementary and practical tool for panelists during olive oil sensory analysis.This study was supported by Fundação para a Ciência e a Tecnologia (FCT),Portugal and the European Community fund FEDER, under the Program PT2020 (Project UID/EQU/50020/2013); under
the strategic funding of UID/BIO/04469/2013 unit; and by Project POCTEP through Project RED/AGROTEC – Experimentation network and transfer for development of agricultural and agroindustrial sectors between Spain and Portugal
Monitoring olive oils quality and oxidative resistance during storage using an electronic tongue
"Available online 4 July 2016"Monitoring olive oils oxidative stability and quality parameters (free acidity, peroxide values, K232 and K270 extinction coefficients) is needed to guarantee that, during storage, their levels remain within the legal thresholds enabling their commercialization as high-value extra-virgin olive oils. Physicochemical levels are assessed using time-consuming routine analytical reference techniques. In this work, the feasibility of a novel approach that merges an electronic tongue and chemometric tools, for monitoring extra-virgin olive oils' quality along one year of storage at dark or exposed to light is discussed. The results confirmed that physicochemical parameters varied with the storage lighting conditions and more significantly with time. Also, multiple linear regression models, using sub-sets of 2228 sensors selected with a meta-heuristic simulated annealing algorithm, allow evaluating the storage time-evolution of olive oils peroxide values, extinction coefficients and oxidative stabilities with satisfactory accuracy (R2 0.98 and 0.96, for leave-one-out and repeated K-fold cross-validation procedures, respectively). The capability of monitoring, in a single electrochemical assay, legal required quality parameters of olive oils, decreases considerable the analysis time and cost, allowing checking the compliance of extra-virgin olive oil quality with labeling. So, the use of electronic tongues for extra-virgin olive oil shelf-life assessment could be envisaged.This work was co-financed by Project POCI-01-0145-FEDER- 006984 e Associated Laboratory LSRE-LCM funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalizaçao (POCI), by national funds through FCT - Fundação para a Ciencia e a Tecnologia; and by the strategic funding of UID/BIO/04469/2013 unit. Nuno Rodrigues thanks FCT, POPHQREN and FSE for the Ph.D. Grant (SFRH/BD/104038/2014)
The use of electronic nose as alternative non-destructive technique to discriminate flavored and unflavored olive oils
Cv. Arbequina extra virgin olive oils (EVOO) were flavored with cinnamon, garlic, and rosemary and characterized. Although flavoring significantly affected the physicochemical quality parameters, all oils fulfilled the legal thresholds for EVOO classification. Flavoring increased (20 to 40%) the total phenolic contents, whereas oxidative stability was dependent on the flavoring agent (a slight increase for rosemary and a decrease for cinnamon and garlic). Flavoring also had a significant impact on the sensory profiles. Unflavored oils, cinnamon, and garlic flavored oils had a fruity-ripe sensation while rosemary flavored oils were fruity-green oils. Fruit-related sensations, perceived in unflavored oils, disappeared with flavoring. Flavoring decreased the sweetness, enhanced the bitterness, and did not influence the pungency of the oils. According to the EU regulations, flavored oils cannot be commercialized as EVOO. Thus, to guarantee the legal labelling requirement and to meet the expectations of the market-specific consumers for differentiated olive oils, a lab-made electronic nose was applied. The device successfully discriminated unflavored from flavored oils and identified the type of flavoring agent (90 ± 10% of correct classifications for the repeated K-fold cross-validation method). Thus, the electronic nose could be used as a practical non-destructive preliminary classification tool for recognizing olive oils’ flavoring practice.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal)
for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020) and to CEB
(UIDB/04469/2020) units and to the Associate Laboratory SusTEC (LA/P/0007/2020), as well
as to BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional
Development Fund under the scope of Norte 2020—Programa Operacional Regional do Norte. Nuno
Rodrigues thanks to National funding by FCT—Foundation for Science and Technology, P.I., through
the institutional scientific employment program-contractinfo:eu-repo/semantics/publishedVersio
- …